Spring Cloud Feign(第四篇)之Fallback

Spring Cloud Feign 之Fallback

環境信息: java 1.8、Spring boot 1.5.10.RELEASE、spring cloud-Edgware.SR3、maven 3.3+

在網絡請求時，可能會出現異常請求，如果還想再異常情況下使系統可用，那麼就需要容錯處理，比如:網絡請求超時時給用戶提示“稍後重試”或使用本地快照數據等等。

Spring Cloud Feign就是通過Fallback實現的，有兩種方式：

1、@FeignClient.fallback = UserFeignFallback.class指定一個實現Feign接口的實現類。

2、@FeignClient.fallbackFactory = UserFeignFactory.class指定一個實現FallbackFactory<T>工廠接口類

因爲Fallback是通過Hystrix實現的， 所以需要開啓Hystrix，spring boot application.properties文件配置feign.hystrix.enabled=true，這樣就開啓了Fallback

Fallback-實現Feign接口

UserFeignFallback回調實現，由spring創建使用@Component(其他的註冊也可以)註解

HystrixTargeter.targetWithFallback方法實現了@FeignClient.fallback處理邏輯，通過源碼可以知道UserFeignFallback回調類是從Spring容器中獲取的，所以UserFeignFallback由spring創建。

UserFeign配置:

package com.example.feign;

import org.springframework.cloud.netflix.feign.FeignClient;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.PostMapping;

import java.util.List;

@FeignClient(name = "user",url = "${user.url}",fallback = UserFeignFallback.class
        /*fallbackFactory = UserFeignFactory.class*/)
public interface UserFeign {

    @PostMapping
    void save(User user);

    @GetMapping("/{id}")
    User getUserByID(@PathVariable("id") String id);

    @GetMapping
    List<User> findAll();
}

UserFeignFallback類：

package com.example.feign;

import org.springframework.stereotype.Component;

import java.util.List;

@Component
public class UserFeignFallback implements UserFeign {

    @Override
    public void save(User user) {

    }

    @Override
    public User getUserByID(String id) {
        User user = new User();
        user.setId("100");
        user.setName("fallback 回調用戶");
        return user;
    }

    @Override
    public List<User> findAll() {
        return null;
    }
}

爲了模擬回調失敗服務提供方，拋出500錯誤。

 @GetMapping("/{id}")
    public User getUserByID(@PathVariable("id") String id) {

//        return userMap.get(id);
        throw new RuntimeException("服務端測試異常！");
    }

運行單元測試UserFeignTest.getUserByID控制檯輸出結果:

2018-08-18 11:47:59.800  INFO 8660 --- [ hystrix-user-1] com.example.feign.UserFeign              : [UserFeign#getUserByID] ---> GET http://localhost:8080/user/1 HTTP/1.1
2018-08-18 11:47:59.800  INFO 8660 --- [ hystrix-user-1] com.example.feign.UserFeign              : [UserFeign#getUserByID] ---> END HTTP (0-byte body)
2018-08-18 11:47:59.828  INFO 8660 --- [ hystrix-user-1] com.example.feign.UserFeign              : [UserFeign#getUserByID] <--- HTTP/1.1 500 (27ms)
2018-08-18 11:47:59.828  INFO 8660 --- [ hystrix-user-1] com.example.feign.UserFeign              : [UserFeign#getUserByID] connection: close
2018-08-18 11:47:59.828  INFO 8660 --- [ hystrix-user-1] com.example.feign.UserFeign              : [UserFeign#getUserByID] content-type: application/json;charset=UTF-8
2018-08-18 11:47:59.828  INFO 8660 --- [ hystrix-user-1] com.example.feign.UserFeign              : [UserFeign#getUserByID] date: Sat, 18 Aug 2018 03:47:59 GMT
2018-08-18 11:47:59.828  INFO 8660 --- [ hystrix-user-1] com.example.feign.UserFeign              : [UserFeign#getUserByID] transfer-encoding: chunked
2018-08-18 11:47:59.828  INFO 8660 --- [ hystrix-user-1] com.example.feign.UserFeign              : [UserFeign#getUserByID] 
2018-08-18 11:47:59.829  INFO 8660 --- [ hystrix-user-1] com.example.feign.UserFeign              : [UserFeign#getUserByID] {"timestamp":1534564079825,"status":500,"error":"Internal Server Error","exception":"java.lang.RuntimeException","message":"服務端測試異常！","path":"/user/1"}
2018-08-18 11:47:59.829  INFO 8660 --- [ hystrix-user-1] com.example.feign.UserFeign              : [UserFeign#getUserByID] <--- END HTTP (167-byte body)
User{id='100', name='fallback 回調用戶'}

服務提供方拋出的500錯誤代碼，但是客戶端程序還可以正常運行輸出了UserFeignFallback.getUserByID方法返回的結果。

FallbackFactory工廠

上面的實現方式簡單，但是獲取不到HTTP請求錯誤狀態碼和信息 ，這時就可以使用工廠模式來實現Fallback

同樣工廠實現類也要交由spring管理，同時結合UserFeignFallback使用，這裏需要注意的create方法返回值類型一定要實現Feign接口，否則會報錯。

UserFeignFactory只做了打印異常處理：

package com.example.feign;

import feign.hystrix.FallbackFactory;
import org.springframework.stereotype.Component;

@Component
public class UserFeignFactory implements FallbackFactory<UserFeign> {

    private final UserFeignFallback userFeignFallback;

    public UserFeignFactory(UserFeignFallback userFeignFallback) {
        this.userFeignFallback = userFeignFallback;
    }

    @Override
    public UserFeign create(Throwable cause) {
        //打印下異常
        cause.printStackTrace();
        return userFeignFallback;
    }
}

UserFeign:

package com.example.feign;

import org.springframework.cloud.netflix.feign.FeignClient;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.PostMapping;

import java.util.List;

@FeignClient(name = "user", url = "${user.url}",
/*fallback = UserFeignFallback.class*/
        fallbackFactory = UserFeignFactory.class)
public interface UserFeign {

    @PostMapping
    void save(User user);

    @GetMapping("/{id}")
    User getUserByID(@PathVariable("id") String id);

    @GetMapping
    List<User> findAll();
}

運行單元測試UserFeignTest.getUserByID可以看到控制檯打印的異常feign.FeignException更多信息省略。

ErrorDecoder接口處理請求錯誤信息，默認實現ErrorDecoder.Default拋出FeignException異常

FeignException.status 方法返回HTTP狀態碼，FallbackFactory.create默認情況下可以強制轉換成FeignException異常這樣就可以獲取到HTTP狀態碼了。

自定義ErrorDecoder

第一種:application.properties

全局配置,通過application.properties配置文件

feign.client.default-config=my-config
feign.client.config.my-config.error-decoder=com.example.feign.MyErrorDecoder

錯誤解碼實現類MyErrorDecoder

package com.example.feign;

import feign.Response;
import feign.codec.ErrorDecoder;

public class MyErrorDecoder implements ErrorDecoder {

    @Override
    public Exception decode(String methodKey, Response response) {
        return new MyFeignException(methodKey,response);
    }
}

自定義異常MyFeignException

package com.example.feign;

import feign.Response;

public class MyFeignException extends RuntimeException {
    private final String methodKey;
    private Response response;


    MyFeignException(String methodKey, Response response) {
        this.methodKey = methodKey;
        this.response = response;
    }


    public Response getResponse() {
        return response;
    }

    public String getMethodKey() {
        return methodKey;
    }
}

第二種:@EnableFeignClients

全局配置,@EnableFeignClients.defaultConfiguration註解

package com.example;

import com.example.feign.FeignClientsConfig;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.netflix.feign.EnableFeignClients;

/**
 * 啓動類
 *
 * @author: sunshaoping
 * @date: Create by in 上午10:47 2018/8/7
 */
@EnableFeignClients(
        defaultConfiguration = FeignClientsConfig.class
)
@SpringBootApplication
public class FeignApplication {

    public static void main(String[] args) {
        SpringApplication.run(FeignApplication.class, args);
    }


}

第三種:@FeignClient

作用範圍是Feign接口,優先級要高於上面兩種，@FeignClient.configuration 註解

package com.example.feign;

import org.springframework.cloud.netflix.feign.FeignClient;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.PostMapping;

import java.util.List;

@FeignClient(name = "user", url = "${user.url}",
/*fallback = UserFeignFallback.class*/
        decode404 = true,
        fallbackFactory = UserFeignFactory.class,
        configuration = FeignClientsConfig.class
)
public interface UserFeign {

    @PostMapping
    void save(User user);

    @GetMapping("/{id}")
    User getUserByID(@PathVariable("id") String id);

    @GetMapping
    List<User> findAll();
}

總結

本章節講了如下內容

Spring Cloud Feign HTTP請求異常Fallback容錯機制，它是基於Hystrix實現的，所以要通過配置參數feign.hystrix.enabled=true開啓該功能，及其兩種實現方式。

Fallback工廠方式引出了ErrorDecoder錯誤解碼自定義處理，有三種方式，可根據實際請求選擇，舉一反三其他自定義配置也可以通過這種方式實現如：Decoder、Encoder、Logger(第二、三章有介紹)。

如果開啓的Hystrix就不要用feign的超時配置了,單位是毫秒

feign.client.config.defalut.connect-timeout=10000

defalut是默認配置名稱，可以使用feign.client.default-config替換自定義名稱

feign.client.default-config=my-config
feign.client.config.my-config.connect-timeout=10000

請使用如下屬性配置超時時間，單位毫秒

hystrix.command.default.execution.isolation.thread.timeoutInMilliseconds=20000

樣例地址 spring-cloud-feign 分支 Spring-Cloud-Feign-之fallback

寫在最後

Spring Cloud Feign 系列持續更新中。。。。。歡迎關注

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